cam iosched: Call cam_iosched_limiter_init() after ios->current is set to the default

Previously ios->current was set to 0 until the first
cam_iosched_cl_maybe_steer() call.

PR: 221954
Obtained from: ElectroBSD
Submitted by: Fabian Keil
Differential Revision: https://reviews.freebsd.org/D12349